Gearing Mechanism for an Injection Device

ABSTRACT

An injection device comprising: a base member ( 102 ); a plunger ( 104 ) for driving a piston in a distal direction; a driving member ( 106 ); and a gear mechanism ( 108 ) providing a gearing between the driving member ( 106 ) and the plunger ( 104 ) such that then the driving member ( 106 ) is moved at a first speed relative to the base member ( 102 ), the plunger ( 104 ) is moved at a second speed relative to the base member ( 102 ); wherein at least two of the base member ( 102 ), the plunger ( 104 ) and the driving member ( 106 ) are pivotally connected to the gear mechanism ( 108 ).

FIELD OF THE INVENTION

The present invention relates to a gear mechanism for an injectiondevice, the gear mechanism comprising a lever mechanism for obtaining agearing. In particular the present invention relates to a gear mechanismcomprising a plurality of pivotally connected members.

BACKGROUND OF THE INVENTION

Syringe devices comprising a gear mechanism are known in the art andexamples may be seen in WO 01/95959 and WO 03/080160. WO 01/95959discloses an injection device for injection of set doses of medicinefrom a cartridge. The syringe device comprises a gearbox which providesa gearing between an axial movement of an injection button and a nutengaging a piston rod relative to a housing. A gear wheel transmissionis established between the nut and the injection button.

It is an object of the present invention to provide a gearing mechanismwhich is more simple than prior art gear mechanisms. A further object ofthe invention is to provide a gear mechanism which enables a wider rangeof obtainable gear ratios as compared to prior art gear mechanisms.

BRIEF DESCRIPTION OF THE INVENTION

In a first aspect of the invention, the invention relates to aninjection device for accommodation of a reservoir comprising a pistonmovable within the reservoir and a medicament to be injected, theinjection device comprising:

-   -   a base member;    -   a plunger for driving the piston in a distal direction;    -   a driving member movable in a proximal direction relative to an        initial position so as to set a dose and movable in a distal        direction towards the initial position so as to eject a dose of        the medicament; and    -   a gear mechanism providing a gearing between the driving member        and the plunger such that when the driving member is moved at a        first speed relative to the base member, the plunger is moved at        a second speed relative to the base member;        wherein the gear mechanism comprises a lever mechanism coupling        a distally directed movement of the driving member with a        distally directed movement of the plunger.

In one embodiment, the gearing mechanism may be so arranged that atleast two of the base member, the plunger and the driving member arepivotally connected to the gear mechanism.

In another embodiment, the gearing mechanism may be so arranged thatboth the base member, the plunger and the driving member are pivotallyconnected to the gear mechanism.

The injection device may be provided as a pen-injector for manuallyadministering set doses of a medicament, where the piston of a reservoiraccommodated in the device is axially moveable upon axially movement ofthe driving member. The driving member is axially movable in the distaldirection responsive to a distally directed push-force exerted by thehand of a user. The push-force may be applied directly on the drivingmember or via one or more intermediate members.

The medicament containing reservoir may form an integral part of theinjection device such that an emptied reservoir cannot be replaced,whereby a user will dispose off the injection device when the reservoirhas been emptied. Alternatively, the device may allow replacement of aused reservoir by a new reservoir or allow the user to change betweenreservoirs containing different kinds of medication and/or the same typeof medication at different concentrations.

The plunger and the piston of the reservoir may be interconnected by apiston rod, which may be locked for movement in the proximal directionsuch that when the plunger is moved in the proximal direction duringdose setting, the piston rod remains in essentially the same positionrelative to the plunger. Moreover, the plunger may be adapted to movethe piston rod in the distal direction during dose ejection, whereby amedicament contained in the reservoir is expelled.

Alternatively, the piston rod is adapted to retract a fixed distance ina proximal direction during an initial phase of a dose settingprocedure, and adapted to move in a distal direction as a dose is beingset.

The gear mechanism provides a gearing between the driving member and theplunger such that when the driving member is moved at a first speedrelative to the base member, the plunger is moved at a second speedrelative to the base member. Accordingly it will be appreciated, thatwhen the driving member is moved a first distance, the plunger is moveda second distance.

In another embodiment the second speed is lower than the first speed,whereby the second distance is shorter than the first distance. Thisprovides the advantage that the gear mechanism converts a relatively lowforce applied to the driving member to a relatively high force appliedto the plunger.

In a further embodiment, the second speed is higher than the firstspeed, whereby the second distance is longer than the first distance.

The gear mechanism may comprise a first, second and third connectingmember each of which is exclusively connected to one of the base member,the plunger and the driving member. In the context of the presentinvention the term “exclusively connected” shall be understood such thateach of the first, second and third connecting member is directlyconnected to only one of the base member, the plunger and the drivingmember, but may be indirectly connected i.e. via one or more elements,to the another of the three elements. As an example, the firstconnecting member may be directly connected to the base member andindirectly connected to the driving member via the second connectingmember.

The connecting members of the gear mechanism each operate in acorresponding plane, e.g. the first connecting member is adapted torotate in a first plane perpendicular to a rotational axis of said firstconnecting member.

In one embodiment the three planes are spaced apart and do not coincide.This provides a gear mechanism wherein none of the connecting memberslimits the rotational movement of another connecting member. In anotherembodiment, two of said three planes coincide, whereby a compactconfiguration may be provided. However, as two of the connecting membersoperate in the same plane, each of said two connecting members islimited in its rotational movement by the other of the two connectingmembers.

In one embodiment the first connecting member is pivotally and directlyconnected to the base member, the second connecting member is pivotallyand directly connected to the driving member, and the third connectingmember is pivotally and directly connected to the plunger. Furthermore,at least one of the second and third connecting members is pivotallyconnected to the first connecting member.

As an example the first connecting member may be pivotally connected tothe base member by means of a first pivotal connection, the secondmember may be pivotally connected to the first member by means of asecond pivotal connection, and the third member may be pivotallyconnected to the first member by means of a third pivotal connection. Asthe each of the second and third connecting members may also beconnected to one of plunger and the driving member, movement of the basemember, the plunger and the driving member are interdependent.

In one embodiment the distance from the third pivotal connection to eachof the first and the second pivotal connections is shorter than thedistance between the first and the second pivotal connections.

By providing the first, the second and third pivotal connections on thefirst connecting member, said member serves as a moment arm. Thus, ifthe first connecting member is allowed to rotate about the first pivotalconnection, a force applied to the second pivotal connection results inan even larger force acting on the third pivotal connection. Hence, ifthe distance between the third pivotal connection and each of the firstand second pivotal connections is identical, a force of 1 Newton appliedto the second pivotal connection results in a force of 2 Newton appliedto the third pivotal connection.

From the above it will be appreciated, that the position of the thirdpivotal connection is decisive for the gearing of the injection device.Hence, in one embodiment the third pivotal connection is provided closerto the first pivotal connection than to the second pivotal connection,and in another embodiment the third pivotal connection is providedcloser to the second pivotal connection than to the first pivotalconnection.

It will be appreciated, that the relationship between the distance fromthe first pivotal connection and each of the second and third pivotalconnections, corresponds to the gearing of the device. Hence, if thedistance from the first pivotal connection to the second pivotalconnection is three times the distance from the first pivotal connectionto the third pivotal connection, a force of 1 Newton applied to thesecond pivotal connection results in a force of 3 Newton acting on thethird pivotal connection.

In one embodiment the first, second and third connecting members haveidentical lengths. Alternatively, at least one of the second and thethird connecting member may be at least 20 percent longer than the firstconnecting member, such as 50 percent longer, such as 100 percent, suchas 150 percent. It will be appreciated, that the longer the second andthird connecting member are relative to the first connecting member, themore linear the gear mechanism is.

In some embodiments the second and third connecting members haveidentical lengths. However it will be appreciated, that the non-linearproperties of the gear mechanism may in some embodiments be reduced byproviding the second and third connecting members at different lengths.As an example the difference in the length of the second and the thirdconnecting member may be at least 20 percent, such as at least 50percent, such as at least 100 percent, such as at least 150 percent.

In one special embodiment the gear mechanism comprises a firstconnecting member pivotally connected to at least two of the basemember, the plunger and the driving member such as to each of the ofsaid three elements. This provides a simplified solution comprising onlyone connecting member. The first connecting member may be arranged tointerconnect both the base member, the plunger and the driving member,the latter three members each being pivotally connected to the firstconnecting member at respective specific locations along the extensionof the first connecting member.

Moreover, at least one of the pivotal connections may be adapted to movealong the first connecting member, e.g. by providing a groove in thefirst connecting member in which the pivotal connection is allowed tomove. Thus, rotation of the first connecting member about one of thethree pivotal connections does not force the slidable pivotal connectionto follow an arc-shaped path. Thereby a mechanism is provided whereineach of the base member, the plunger and the driving member is moveablealong respective rectilinear paths, the paths being mutually parallel.When the rotatable part of the base member, the plunger and the drivingmember are forced to rotate around the longitudinal axis of the device,their mutual spacing in directions normal to the longitudinal axisremains fixed.

Furthermore, the base member may comprise a fixed part and a rotatablepart, the fixed part being rotationally and translationally retained inrelation to a housing of the device, the rotatable part being adapted torotate relative to the base member about a longitudinal axis of the basemember, the rotatable part furthermore being translationally retained inrelation to the fixed part.

In a still further embodiment, the driving member is rotatably mountedwith respect to the fixed part of the base member, and hence, rotatablymounted relative to a housing of the device. The driving member may beadapted to be lifted in the proximal direction of the device as afunction of its rotation, such as provided by a threaded coupling. Insuch an embodiment, the driving member is moved axially in the proximaldirection in accordance with the size of the dose being set by rotatingthe driving member with respect to the housing.

Moreover, a clutch may be provided between the driving member and thefixed part, said clutch may be adapted to be changed between:

-   -   a coupled position wherein a threaded inner surface of the        clutch engages a threaded outer surface of the fixed part such        that when the driving member is rotated, the threaded engagement        causes the driving member to be moved in a proximal direction,        and    -   a decoupled position wherein the threaded inner surface of the        clutch disengages the threaded outer surface of the fixed part,        so as to allow translational and non-rotational movement between        the driving member and fixed part.

In a still further embodiment, the driving member, and optionally, theplunger, is/are adapted to also rotate during their translationalmovement during injection.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 disclose two extreme positions of a first embodiment ofthe gear mechanism according to the invention,

FIG. 3 discloses a second embodiment of the gear mechanism, and

FIG. 4 discloses a third embodiment of the gear mechanism.

FIGS. 1 and 2 disclose a dosing assembly 100 for a syringe device, suchas a pen based injector. The dosing assembly 100 described below isconfigured for inclusion in an injection pen having a dosing scheme ofthe kind disclosed in WO 01/95959, this reference hereby beingincorporated by reference. The gear mechanism 108 described belowsubstitutes the tooth and rack based gear-box arrangement of theembodiments shown in the figures of WO 01/95959.

FIGS. 1 and 2 disclose two extreme positions of the gear mechanism. FIG.1 illustrates the dosing assembly 100 in its initial position wherein nodose is set, and FIG. 2 illustrates the dosing assembly 100 when amaximum dose has been set.

The dosing assembly comprises a base member 102, a plunger 104 and adriving member 106. The plunger 104 and the driving member 106 aremovable in an axial direction relative to the base member 102. Moreover,the distance between the base member 102, the plunger 104 and thedriving member 106, remains essentially constant during dose setting andejection of a dose. The base member comprises a fixed part 101 and arotatable part 103.

The plunger 104 and the driving member 106 are pivotally connected tothe base member 102 via a gear mechanism 108. The gear mechanism 108comprises a first connecting member 110, which in a first end ispivotally connected to the base member 102 by means of a first pivotalconnection 112 and in a second end is pivotally connected to a secondconnecting member 114 via a second pivotal connection 116. Moreover, thefirst connecting member 110 is pivotally connected to a third connectingmember 118 via a third pivotal connection 120. Furthermore, the secondconnecting member 114 is pivotally connected to the driving member 106via a fourth pivotal connection 122, and the third connecting member118, is pivotally connected to the plunger 104 via a fifth pivotalconnection 124.

The fixed part 101 is retained rotationally and translationally inrelation to a housing of the device. Furthermore, the rotatable part 103is adapted to be rotated about its longitudinal axis, while beingretained translationally in relation to the fixed part 101. Moreover, aclutch 105 of the driving member is adapted to be changed between acoupled position wherein it engages a threaded outer surface 107 of thefixed part 101, and a decoupled position wherein it does not engage thethreaded outer surface 107. When the clutch is in its decoupled positionthe driving member 106 is allowed to move in the distal direction 130without rotating, as the clutch is disengaged from the threaded outersurface 107.

In order to set a dose, the driving member 106 is rotated about thelongitudinal axis of the device. The rotational movement causes thedriving member 106 to be moved in the proximal direction due to theengagement between the clutch 105 and the threaded outer surface 107.

As the second connecting member 114 is pivotally connected to thedriving member 106, the proximal movement of the driving member 106causes the first connecting member 110 to rotate about the first pivotalconnection 112, as indicated by arrow 128. Due to the rotation, thethird connecting member 118 is also forced in the proximal direction126. As the third pivotal connection 120 is located closer to the firstpivotal connection 112 than the second pivotal connection 116, theplunger 104 is moved at a slower speed relative to the base member 102than the driving member 106. It will be appreciated that the closer thethird pivotal connection 120 is to the first pivotal connection 112, theslower the speed of the plunger 104 is relative to the speed of thedriving member 106.

In one embodiment the plunger 104 comprises a threaded inner surface(not shown) which is adapted to engage a threaded outer surface of thepiston rod (not shown). Moreover, rotational and translational movementof the driving member 106 during dose setting causes rotational andtranslational movement of the plunger 104. However as described in theaforementioned, the plunger 104 is moved at a slower translationalspeed, and, thus, in order to maintain the piston rod in substantiallythe same position during dose setting, the pitch of the thread of thepiston rod must be decreased correspondingly relative to the pitch ofthe threaded outer surface 107.

Alternatively, the plunger 104 is arranged to cooperate with a pawl andratchet mechanism (not shown) which provides for telescopicallyengagement between the plunger 104 and the piston.

In an embodiment, a dose setting drum (not shown) is operationallycoupled to the driving member 106 for rotating the driving member 106during dose setting. Additionally, an injection button (not shown)axially extending from the proximal end of the injection device isoperationally coupled to the driving member 106 for axially moving thedriving member 106 upon manually pushing of the injection button in thedistal direction. Said dose setting drum and injection button may beprovided as mutually separate members or alternatively, these elementsform one unitary member.

FIG. 2 illustrates a situation wherein a dose is set and the device isready for ejection of a dose. In order to eject a dose, the clutch ischanged to its decoupled position, whereby the driving member is allowedto move in the distal direction without rotating, as the clutch does notengage the threaded outer surface. The plunger 104 cooperates with apiston rod (not shown) such that when the plunger is moved in the distaldirection 130, the piston rod forces a piston (not shown) in a distaldirection whereby a medicament contained in a reservoir (not shown) isexpelled.

It will be appreciated that by using the driving member 106 to eject themedicament, the first connecting member 110 serves as a moment armwhereby a relatively small force need be applied to cause the plunger tomove in the distal direction 130. Again it will be appreciated, that thecloser the third pivotal connection 120 is to the first pivotalconnection 112, the smaller a force need be applied to the drivingmember 106 in order to move the plunger 104. Moreover it will beappreciated, that due to the different speeds, the plunge 104 is moved ashorter distance relative to the base member than the driving member106, for any angular movement of the first connecting member 110 aboutthe first pivotal connection.

Additionally, it will be appreciated that the gearing between theplunger 104 and the driving member 106 is determined by the length ofthe first connecting member 110 and the relative position of the first,second, and third pivotal connection 112,116,120 on said firstconnecting member 110.

FIGS. 3 and 4 disclose a second and third embodiment of the gearmechanism 108. The two embodiments comprise a plunger 104 and a drivingmember 106 which are movable relative to a base member 102.

The gear mechanism 108 comprises a first connecting member 110, which ispivotally connected to the base member 102, the plunger 104 and thedriving member 106, via a first pivotal connection 112, a fifth pivotalconnection 124, and a fourth pivotal connection 122, respectively.

In FIG. 3, the first connecting member 110 comprises a first and secondgroove 132, 134 allowing the first pivotal connection 112 and the fourthpivotal connection 122 to move in a longitudinal direction of the firstconnecting member 110 between a first and second position 136,138. Thefifth pivotal connection 124 is locked for longitudinal movementrelative to the longitudinal direction of the first connecting member110. All three pivotal connections allow the first connecting member 110to rotate about each of the pivotal connections 112,122,124, such thatthe first connecting member 110 may pivot relative to the base member102, the plunger 104 and the driving member 106.

In one embodiment the mutual distance between the base member 102, theplunger 104 and the driving member 106, in directions normal to thelongitudinal axis, remains essentially constant during dose setting andejection of a dose. Accordingly, it will be appreciated that when thedriving member 106 is moved in the proximal direction 126, the fourthpivotal connection 122 is moved in the direction of the first position136, until the first connecting member 110 is at right angle to theplunger 104. Upon further proximal movement of the driving member 106,the fourth pivotal connection 122 is moved away from the first position136 and towards the second position 138. In order to reduce the frictionbetween the pivotal connections 112,122 and the inner surfaces of thegrooves 132,134, said inner surfaces may have a smooth surface with alow coefficient of friction. Alternatively, or as a supplement, bearingsmay be provided on the pivotal connections 112,122. In yet anotheralternative, the pivotal connections and the grooves are lubricated soas to reduce the friction between the engaging surfaces.

In FIG. 4 the grooves 132,134 are merged such that two pivotalconnections 122,124 are allowed to move in the longitudinal direction ofthe first connecting member 110, whereas the first pivotal connection112 is locked for longitudinal movement relative to the first connectingmember 110. It will be appreciated that in some embodiments the grooves132,134 need not be merged in order to enable the gear mechanism towork.

It will be appreciated, that most of the description of the gearmechanism of FIG. 3 also applies to the gear mechanism of FIG. 4.

While the dosing assembly according to the above embodiments have beendescribed with reference to the general dosing scheme of WO 01/95959, itshould be stressed that the present invention is not limited to thisparticular dosing scheme. The gearing arrangement according to thepresent invention is further adoptable in pen-injectors having variouskinds of dosing schemes, such as the ones described in WO9938554,WO2006114395, WO2006114396, US20040215152, U.S. Pat. No. 5,584,815 andU.S. Pat. No. 4,883,472, however, this list being non-exhaustive.

1. A pen-injector for manually administering set doses of a medicament,the injector adapted for accommodating a reservoir comprising a pistonmovable along a first axis within the reservoir and a medicament to beinjected, the pen-injector comprising: a base member; a plunger fordriving the piston axially in a distal direction; a driving memberaxially movable relative to the base member, the driving member movablein a proximal direction relative to an initial position so as to set adose and manually pushable in a distal direction towards the initialposition so as to eject a dose of the medicament; and a gear mechanismproviding a gearing between the driving member and the plunger such thatwhen the driving member is moved at a first speed relative to the basemember, the plunger is moved at a second speed relative to the basemember; wherein at least two of the base member, the plunger and thedriving member are pivotally connected to the gear mechanism.
 2. Apen-injector according to claim 1, wherein the gear mechanism comprisesa first, second and third connecting member each of which is exclusivelyconnected to one of the base member, the plunger and the driving member.3. A pen-injector according to claim 2, wherein the first connectingmember is pivotally connected to the base member, the second connectingmember is pivotally connected to the driving member, and the thirdconnecting member is pivotally connected to the plunger, and wherein atleast one of the second and third connecting members is pivotallyconnected to the first connecting member.
 4. A pen-injector according toclaim 3, wherein the first connecting member is pivotally connected tothe base member by means of a first pivotal connection, the secondmember is pivotally connected to the first member by means of a secondpivotal connection, and the third member is pivotally connected to thefirst member by means of a third pivotal connection.
 5. A pen-injectoraccording to claim 4, wherein the distance from the third pivotalconnection to each of the first and the second pivotal connections isshorter than the distance between the first and the second pivotalconnection.
 6. A pen-injector according to claim 5, wherein the distancebetween the third pivotal connection and the first pivotal connection isshorter than the distance between the third pivotal connection and thesecond pivotal connection.
 7. A pen-injector according to claim 5,wherein the distance between the third pivotal connection and the firstpivotal connection is longer than the distance between the third pivotalconnection and the second pivotal connection.
 8. A pen-injectoraccording to claim 2, wherein at least one of the second and the thirdconnecting member is at least 20 percent longer than the firstconnecting member.
 9. A pen-injector according to claim 2, wherein thedifference in the length of the second and the third connecting memberis at least 20 percent.
 10. An pen-injector according to claim 2,wherein the second speed is lower than the first speed.
 11. Apen-injector according to claim 1, wherein the gear mechanism comprisesa first connecting member pivotally connected to at least two of thebase member, the plunger and the driving member.
 12. A pen-injectoraccording to claim 11, wherein the first connecting member is pivotallyconnected to the base member, the plunger and the driving member.
 13. Apen-injector according to claim 2, wherein the base member comprises afixed part and a rotatable part, the fixed part being rotationally andtranslationally retained in relation to a housing of the device, therotatable part being adapted to rotate relative to the base member abouta longitudinal axis of the base member, the rotatable part furthermorebeing translationally retained in relation to the fixed part.
 14. Apen-injector according to claim 13, further comprising a clutch providedbetween the driving member and the fixed part, said clutch being adaptedto be changed between: a coupled position wherein a threaded innersurface of the clutch engages a threaded outer surface of the fixed partsuch that when the driving member is rotated, the threaded engagementcauses the driving member to be moved in a proximal direction, and adecoupled position wherein the threaded inner surface of the clutchdisengages the threaded outer surface of the fixed part, so as to allowtranslational and non-rotational movement between the driving member andfixed part.
 15. A pen-injector according to claim 8, wherein at leastone of the second and the third connecting member is 50 percent longerthan the first connecting member.
 16. A pen-injector according to claim9, wherein the difference in the length of the second and the thirdconnecting member is 50 percent.